Since Danger Mouse (DM) is SUPER CHEVY's in-house test engine and we vowed long ago to test any combinations suggested to us, this month is our first example of mixing the wrong components. The culprit here is not a bad part. Rather, the culprit is the improper selection of a combination of parts. Last month, we said we'd swap cylinder heads to see if the stock GM camel hump castings were keeping DM from making more power. Since the inception of DM, we've received many letters from readers suggesting we equip it with a set of World Products S/R Torquer cylinder heads to help out in the horsepower arena. We did just that but did not make any other adjustments in conjunction with the new heads. As with any swap you make, how your upgrades work with each other is the determining factor in whether or not your "better" part is actually "better" for your current setup (or whether you'll need to make some adjustments in order to use your better part). The root of the power loss we suffered came from the fact that the S/R Torquer heads (S/R stands for "stock replacement") were bigger than the stock GM heads in all the critical areas. And on a low-rpm street motor like DM, bigger is not better. The S/Rs had larger combustion chambers (67 cc vs. 62 cc on the milled 461 castings we'd been running) and larger valves (2.02/1.60 vs. 1.94/1.50). The large combustion chamber dropped Danger Mouse's compression ratio 1/2 point, putting it just below the 9:1 mark, and the larger valve sizes, particularly on the intake side, probably reduced charge velocity enough to hamper the cylinder's filling at low speeds.

3/13

Improper cylinder head selection resulted in less power and torque. Although the net result of our test wasn't a horsepower gain, it proved a positive lesson in choosing the correct parts.

What We LearnedAll this month's test proved is that it's extremely critical to know exactly what parts you have before you start replacing them. That might mean having your car sit in the garage for a few days while you remove the heads and measure everything prior to ordering the new parts. But that's the only way to be sure you won't be taking a step in the wrong direction. Had DM originally been equipped with a set of heads that had big 76cc chambers, the S/R heads would have boosted compression and that would have probably made more power. Also, if DM was a higher-rpm engine or had more cubic inches, ala stroker 383, it could have made good use of the S/R's larger valves as well. Even though we know we could mill the S/R heads to get an equal compression ratio and re-test them to see the results, we'd rather not start modifying parts this early. Instead, we'll box up the S/R heads and re-test them again another time when DM's got either more inches or more rpm to play with.

MORE PHOTOS

Improper cylinder head selection resulted in less power and torque. Although the net result of our test wasn't a horsepower gain, it proved a positive lesson in choosing the correct parts.

To seal the new cylinder heads we installed Mr. Gasket's MLS head gaskets. The MLS stands for "Multi-layered-steel" (PN 3130G), and as the photo shows, the gaskets are made from three layers of steel shim that, when compressed, are 0.040 inch thick. No sealers are needed, and they don't have to be retorqued.

This was the first time the heads have been off DM since its first dyno bashing several months ago. The burn patterns on the pistons look good, and there are no signs of any fatigue or wear in the bores or on the Motown block.

Mr. Gasket also supplied its new 1/16-inch-thick Ultra-Seal II intake gaskets (PN 810G) to seal the Edelbrock Air Gap manifold to the iron World Products heads. These gaskets are reusable, and as of this writing, we've swapped intakes about six times, using the same set of gaskets, without any leaks.

To keep testing consistent we used the same Edelbrock Air Gap RPM manifold as we did with the factory heads.

The World Products S/R Torquers feature guided pushrod slots so no guideplates were needed.

We equipped DM with the same set of COMP Cams 1.5:1 roller rocker arms for this test.

These heads are named S/R Torquers for a reason. The "SR" stands for stock replacement, and the combustion chambers replicate stock heads so they can pass emissions testing without a hitch. Unfortunately, these chambers were also larger than DM's stock heads, so compression fell off by 1/2 point.

Overall, the S/R Torquers are great heads. They'd be especially helpful to you if you were replacing a set of factory heads with 76cc chambers, although, they're also available in that size if you don't want to increase your compression.

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